Flooding: Pay Me Now or Pay Me Later

I majored in geology in college and despite running for the hills after two years of graduate school, I maintained a perfect GPA while working on a Masters Degree in geochemistry. I studied hard and took school very seriously. I actually enjoyed the material and found my latter years in college and my time in grad school to be yet another outlet for my competitive nature. Sure, I was cocky at times, no doubt about it, but I really had a passion for the subject matter and my exuberance helped buy me some forgiveness with professors and guest lecturers.

Waking up to news this morning that the levee in New Orleans has been topped and that the town of Port Arthur in Texas is protected by a seawall of merely 14 feet in height -- and expects a storm surge of 20 feet -- got me thinking back to a guest lecturer I had a brief run-in with in college. The Department of Geology at Lafayette College in Easton, PA featured weekly lunchtime presentations dubbed the "Brown Bag" series and as majors in the department, we were all but required to attend.

One such presenter was a hydrologist from the New South Wales area of Australia. He was there to talk about the Warragamba Dam that was built to protect Sydney's population from a 700-year flood. For those unfamilliar with this terminology, a 700-year flood doesn't necessarily mean that it will only happen once every 700 years (or ever for that matter) but that there is a 1:700 chance of a flood of that magnitude occuring during any given year. It is entirely possible (although unlikely) to experience a 700-year flood every year for 5 years in a row.

The way in which flood frequency is determined is through plotting the occurrence of all such events over time and extrapolating from there. For example, one could plot the measured flood stage of a given river against time. By determining how often a given flood stage is seen to occur, one could extrapolate a curve to show what the expected flood stage of a future catastrophic flood may be. In other words, by knowing that the river has risen to a height of 6 feet above flood stage every 10 years, and 12 feet above flood stage every 20 years, we could assume that a flood of 24 feet may be in order every 40 years. Of course, this would assume a perfectly linear relationship, but nevertheless it is a way of addressing and planning around our limited knowledge base -- we haven't been monitoring rivers (or storms for that matter) for hundreds of years so extrapolation is vital.

And this is where cultures collide.

Our speaker that day argued that building a dam to protect from a flood with a 1:700 chance of occuring wasn't good enough. He felt the data should be exrapolated further and that the Australian government should have determined what the flood stage for a 1500-year flood would be and built the dam to hold it back. To illustrate his point, he had drawn a quick graph on the overhead transparency showing a perfectly linear relationship between rainfall and time and extended the line out and up off the graph to where he felt Sydney needed to be in order to guarantee the public's safety.

He took this opportunity to critique the United States for allowing all of our safety decisions to be too heavily influenced by cost-to-risk analyses. He commented that many of the levee systems and dams constructed in the United States were built to protect against a 100-year storm or flood and only a scant few projects offered protection against an event with a 1:250 chance of occuring. He made several comments about the Army Corps of Engineers placing too low of a value on American lives.

It was at this time that I spoke up. I pointed out to him that assuming an indefinitely linear relationship between expected rainfall and time was senseless. I inquired if his plan for protecting against a 1500-year storm also required the government to provide each citizen with an ark and a pair of llamas. Obviously, a reasonable scientist or layman could come to the conclusion that eventually you will reach a point when it simply has to stop raining. That the curve is not linear, but rather asymptotic, and that a limit will inevitably be reached. We will eventually see the curve flatten and that there would be no measurable difference between a flood or storm that occurs once every 600 years and one that occurs every 2000 years.

My thesis advisor, and nationally recognized geomorphologist and hydrologist, nodded his head approvingly. He agreed with me. And if he felt that the US was off-the-mark with its conservative flood protection policies, he didn't let it show.

The presenter that day simply shook his head understandably to my comments as if he had heard them everywhere he went, and simply replied by stating that he doesn't think a 1500-year storm will occur, but he couldn't help but feel the lives of those living in Sydney were worth the construction expense. Even if it was just for peace of mind.

Watching the horror unfold in New Orleans over the past several weeks and seeing another low-lying area on the Gulf Coast brace for more of the same from Hurricane Rita, I sit here wondering if perhaps our Aussie presenter was on to something. It's highly understandable for us as a nation to allow construction costs to enter into the equation, and certainly nobody wants 50 foot seawalls marring the landscape. But obviously our plans are flawed. We are spending far too much money rebuilding areas than simply protecting them. The answer must lie somewhere between our current standards and those of the whatever-it-takes presenter I listened to that day. When tragedy strikes we mustn't simply rebuild what was broken, but rather improve on it. Learn from it. Extrapolate further into the future and build to protect against that.

And then when the construction is complete and everyone is safe, find yourself an Aussie and give him a big hearty American "good on ya' mate!'

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